Use of Pt/M(UPD) (M  Pb, Tl, Bi) modified electrodes to the catalytic electroreduction of heterocyclic nitro compounds—I. 3-nitro-1H-1,2,4-triazole

Abstract

Platinum UPD modified electrodes (Pt/M(UPD), where M  Pb, Tl, Bi) have been used to study electroreduction of 3-nitro-1H-1,2,4-triazole (NTr) in aqueous acid, alkaline and intermediate pH buffer solutions. At these modified electrodes, NTr undergoes a four-electron reduction which occurs via electron-transfer mechanism and not by hydrogenation mechanism as occurs at Pt itself. In strongly acid solutions the electrode process follows the ECCE sequence with the second chemical reaction being responsible for kinetically-controlled limiting currents. The slow chemical step in the ECCE sequence is a dehydration reaction of the N,N-dihydroxyamine intermediate. The kinetics of this homogeneous chemical reaction has been studied as a function of temperature and solution pH by using rotating disc data. Moreover, polarographic data for NTr are also given in this paper. In strongly basic media, the Pt/M(UPD) surfaces exhibit an unexpected enhanced catalytic activity for the nitro-group electroreduction compared to that of mercury.